Resistance element



March 7, 1939. KMLEDERER Em ,1 9

RES ISTANGE ELEMENT Filed April 20, 1936 l I l? J6 Z0 3 1 SSJR- 35: J6 1 35 I Z5 i1 ZZ I Kl-a- Patented Mar. 7, 1939 ,hilTED sm'rrs BESKSTANCE ELEMENT Karl M. Lederer, Newark, and Alexander Dempster, Linden, N. 3., assignors. to Weston Electrical Instrument Corporation, Newark, N. 1.,

a corporation of New Jersey Application spruce, 1936, Serial No. 75,440

9 Claim.

This invention relates to resistance elements and particularly to resistor bulbs'for usein the electrical measurement of temperatures.

" The resistor bulbs fortemper'ature measurements are small units which may-be secured to an object,'such as an engine or carbureter, for

obtaining a continuousmeasurement of tempera ture by observing the variation of current flow through the resistor bulb as the resistance theren of varies with temperature. The small size of these units has made it diilicult to'obtain good electrical insulation and a to an enclosed resistance winding.

An object of this invention is to provide an is enclosed resistance element which is adequately insulated from its support and an enclosing shell, and which responds rapidly to temperature changes at the exterior oi. the shell. An object is to provide a resistor bulb in which a bare rego sistance wire is insulated from its metailic support by a thin layer of metallic oxide that is formed upon the metallic support. Another ob-- ject is to provide a resistor bulb in which the resistance wire is formed as a relatively short- 25 length of a single layer coil of small diameter and small pitch, and this short length of closely coiled wire is wound on the grooved surface of a supporting tube. More particularly, an object is to provide a resistor bulb of the type including a so mounting head carrying a tubular shell or container within which the resistance is located, the

resistance being a bare wire wound upon a grooved aluminum tube that carriesan insulating film of aluminum oxide.

, 35 These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. l is an enlarged longitudinal section 40 through the mounting head and shell of one -embodiment of the invention, other parts being shown in elevation,- and a portion of the connecting cable being also shown; Fig. 2 is a similar sectional view, at right angles 45 to Fig.1, of the insulating spool and the resistance element of the resistor bulb;

'Fig. 3 is a plan view of the insulating spool and the terminal plugs mounted thereon Fig. 4 is a fragmentary sectional view, on a 50 still larger scale, through the lower end of the resistor bulb; and

Fig. 5 is a fragmentary sectional view through another embodiment of the invention.

- In the drawing, the reference numeral I iden- 55 titles the central enlarged section of the-mount good heat transfer ing head of the resistor bulb, this section being of hexagonal form or provided with grooves or recesses ior taking a wrench by which the adjacent threaded section 2 of the head may be threaded into an opening in the water jacket or 5 oil case of an engine, into the wall of a carburetor air inlet, or into any other object or fluid container where temperature measurements are desired. The threaded section 2 merges intoa thinwalled shell 3 that The upper end 4 of the mounting is a threaded sleeve which receives the bushing, 5 by which the connecting plug 6 of a cable "I may be secured within the sleeve 4 of the resistor bulb. -Metallic sleeves 8 within the plug 6 are provided with screws 9 at their outer ends for securing the cable wires to the sleeves, and the lower ends of the sleeves have a clbse sliding fit upon the friction plug terminals ID of the resistance element.

The plug terminals l0 extend through a spool 4 H of insulating material, preferablya ceramic vmaterial if the resistance bulb is to be used at elevated temperatures, which is retained within the mounting head by a splitring l2. A vent opening I3 extends through the mounting head at the level of the'upper surface of the spool H to prevent accumulations of oil or moisture adjacent the plug terminals I I]. This vent is important in many instances as the outer ends of the resistor bulbs are frequently so located that oil or water may seep into the mounting head and aiiect the insulation of the terminals. v

A thin tube 14 is cemented or otherwise se- -cured to the lower reduced diameter portion or spool H, and extends to or approximately to the lower end of the shell 3. The lower portion of the tube l4 has a double helical thread or parallel grooves formed in its outer surface and the winding l5 of resistance wire is located within these grooves. "The lower end of the tube has two adjacent notches l6 which provide an anchor for the central portion of the winding, see Fig. 2. As best shown in Figs. 4 and 5, the resistance wire is first formed into a close coil or single layer solenoid of small diameter and small pitch, thus 4 substantially reducing the efiective length of, the winding which is to be placed upon the tube. This reductionin length is particularly advantageous when the winding is looped back upon itself ahd formed as a dual winding to place both terminals at the upper portion of the tube.

The actual length of the resistance wire is several feet but the close? coiling may reduce this to an effective length of less than one foot of winding material that is to be placed within the is closedat" its lower end. 10

grooves of course, to apply of the tubular support. It is pomble, the resistance, wire in the customary form of a simple single layer helix and this type of winding will be quite satisfactory in'the case of low resistanceunits. l

I v'I'he upper uncoiled ends I! of the resistance wire l5 aresecured beneath, clamped, welded or l1 on screws ll' which are ll and thread into the lower --to the temperature-resistance variations of copper. When the entire resistance is provided by thelwire l5,'the stub terminal I8 is directly connected to a terminal lug IS on he second connecting terminal Hi. "It is desira le', however, to form the resistance I5 of a material, such as nickel, having a higher resistance than copper.

This permits the use of a larger size or a shorter length of the nickel resistance wire, but a compensating winding of wire having a substantially zero temperature-resistance characteristic must minal l8 and the terminal lug I9.

and claimed in the copending application of Karl M. Lederer, Ser. No. 75,441, filed April 20, 1936, the characteristics of a standard copper wire re- 'end be used with a nickel wire resistance if the resistor bulb is to be interchangeable with the standard copper wire resistances. Thiscompensating winding 20 of manganin is wound upon the spool ii and connected, between the stub ter- As described sistor bulb having a resistance of 100 ohms at 25 C. may be obtained when the nickel wire 15 hasa resistance of ohms at-25.C. and the manganin wire'20 has a resistance of 35 ohms.

The clearances between the tube H and the shell 3 are preferably held to minimum values transfer between the ex-. terior-of the shell and greater clearance is provided between the upper of tube It and the mounting sleeve 2 and avoid a heat transfer at this section. It is possible to form the tube material when a bare wire I! is used, and the resistor bulb will not be subjected to'high temperatures. The mounting head and integral sleeve 3 may be formed of steel or Monelmetal, lei-Cass, or alumin' um alloys'as e Preferably, however, the tube II and the sleeve 21 are formed of aluminum that has been treated by' known electrolytic processes to-form a substantially continuous insulating film of aluminum oxide on and in situ from the metal at those parts whichcontact or may contact with the bare-resistance wire. This insulating film isso that it cannot be shown in Figs. 1 and 2, but it is shown in the enlarged scale view, Fig.4, as a coating I la on the aluminum tube I4 and a gloating'fla on the inner surface of the aluminum eeve ever, as the thickness of the oxide coatinghas been exaggerated for clearness of illustration.

- Thepitch of the closely'coiled wire i5 is, of

course, substantially of the bare wire to prevent iacent turns.

As shown in Fig. be provided such that the greater than the diameter short-circuiting of ad- 5, a simpler construction may shell itself may be of a metal that Iii" of one of the connecting terminals the resistance wire,'but

ll of a molded plastic andto use a thin insulating sleeve 2] of the same 21. This view is not toexactscale, howwhen the design requirements are ment to form a him of aluminum oxide inner surface of the shell for insulation of the bare wire ii. The integral shell construction of Fig. 1 may be employed, or alternatively, the, aluminum shell 3' may be secured to a steel mounting head. Where conditions permit, the vacant space in the grooves may be filled either with a material I!" such as powdered asbestos, plaster Vaseline as thereby the heat response andinsula- 7 tion will be improved materially.

As shown in Fig. 1, one or may be formedin the mounting head I to receive a wire that may be secured to a stud'on the en-' gine by. a lead seal to prevent an unauthorized removal of the resistor bulb.

The material and form of shell 3 affect the heat transfer and the, response of the resistor bulb and, so far as'is practical, the thickness-of these parts should be reduced to a minimum. As a wall thicmess for winding section and the support 0.010 inch, with a wall thickness of inch for the housing shell 3, has been i factory for general conditions of use. grooved section which carries the resistance wire should preferably be spaced at least one-half inch from the mounting head and threaded sleeve 2 to reduce the heat ving head and the wire. r Attention is directed to the fact that a sumewhat simpler terminal construction may be employed when the entire resistance is provided by the winding l5. Each terminal plug lilmay then have the extension ill for connection to the winding i5 when the used. The assembly operations are :somewhat simpler and the resistance wire is more securely ,sealed when the mountinghead and shell 3 are formed in one piece. e

We claim:

1. A resistor bulb ment of temperature comprising a metallic support, a resistance tube 'il, between the grooved spool I I, of about about 0.015

und satis- The shell Iflmay in. on theof Paris or grease and V more passages 22 an example, it may be stated that for the electrical measurethe-tube ,and the I transfer between the mountcompensating winding 20 is not 50' I. wire of relatively high temperature coefllcient of resistance wound on said su'pport, a film of non-conducting metallic oxide on and formed from the metal of said support, a shell in heat transfer relation to said'resistance wire and enclosing said support and resistance wire; means for supporting said shell in heat transfer relation to the material whose temperature is to be measured, and a substantially continuous film of non-conducting metallic oxide within said shell and-insulating the. resistance wire therefrom.. 2. A' resistor bulb for theelectrical measurement of temperatures comprising a-thin-walled tubular aluminum support, abare resistance wire of relatively high temperature-resistance coemcient wound on said support, a non-conducting aluminum oxide film on' and formed from the metal of said support to insulate the wire therefrom, and a thin-walled in intimate heat transfer relation to said wire and closely encloswire, whereby said wire L ing said support and quickly assumed the temperature of the medium surrounding saidshell and its resistance thereby w fluctuates as a function of that temperature. v 3. A resistor bulb for-the electrical measurea from the in the portion of ance wire is aluminum, and the film of aluminum adjacent coils of said wire and ment of temperatures comprising an aluminum tube having a helically grooved surface, a bare resistance wire of finite and predetermined temperature-resistance characteristic wound upon said tube in the grooved surface thereof, a nonconducting film of aluminum oxide on and formed metal of said tube to insulate the wire therefrom, a metallic shell enclosing said tube and in intimate heat transfer relation to the wire thereon, means for mounting the shell on and in good heat transfer relation to an object whose temperature is to be measured, and insulating means comprising a substantially continuous film of aluminum oxide separating said wire from said shell.

4. The invention as claimed in claim 3, wherein said insulating means includes an aluminum sleeve surounding said winding of resistance wire and the adjacent portion of said tube, the interior surface of said sleeve having an adherent oxidiaed surface constituting said fllm of aluminum oxide.

5. The invention said shell adjacent said resistoxide insulating the same from the winding is an adherent layer on the interior of said portion of the shell. Y

6. A resistor bulb having a resistance that varies as a predetermined factor of its temperature for use in the electrical measurement of temperatures, said resistor bulb comprising a tubular aluminum member having a layer of aluminum oxide formed in situ on the exterior surface thereof, said member having a thin wall and being helically grooved at the exterior of one end portion thereof, and a multiple turn winding of closely coiled bare resistance wire in the grooves and entirely within the exterior surface of said member, adjacent turns oi said winding, respectively, being spaced from each other as claimed in claim 3, where- 7. In a resistor bulb, a hollow mounting head terminating in a shell having a closed inner end, a spool of insulating material within the said head, a pair of connecting terminals on said spool for making connections to an external circuit, a

stub terminal on said spool, a temperature-vari-w ant resistance having the ends thereof connected to said stub terminal and one of said connecting terminals, means supporting said resistance within the inner end of said shell and closely adjacent the circumferential wall thereof, and a temperature-invariant resistance on said spool, the ends of said temperature-invariant resistance being connected to said stub terminal and to the second of said connecting terminals.

8. A resistor bulb as claimed in claim 7, wherein said supporting means comprises a tubular member carried by said spool and having the tem perature-variant resistance wound on the exterior surfce thereof, and the said stub terminal and the first of said connecting terminals extend into said tubular member.

9. In a resistor bulb, the combination with a tube having a resistance wire thereon and insulated therefrom, of a mounting head having an externally threaded sleeve projecting from one side thereof, said sleeve terminating in an integral tubular shell, said shell having a closed inner end, a threaded sleeve integral with and projecting from the other side of said mounting head for receiving a cable plug, a passage extending through said head to connect the bores of said sleeves, a disk of insulating material secured in said passage and supporting said tube within said shell, and terminals for said resistance wire supported by said disk within the second sleeve for engagement with complementary terminals on a cable plug.

KARL M. LEDERER. AIEXANDER DEMPS'I'ER. 

